ltm2884 – isolated usb transceiver with isolated power€¦ · vlo2 vlo2 regulated output voltage...

LTM2884

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For more information www.linear.com/LTM2884

Typical applicaTion

FeaTures DescripTion

Isolated USB Transceiver with Isolated Power

The LTM®2884 is a complete galvanically isolated USB 2.0 compatible μModule® (micromodule) transceiver. An upstream supply powers both sides of the interface through an integrated, isolated DC/DC converter.

The LTM2884 is ideal for isolation in host, hub, bus split-ter or peripheral device applications. It is compatible with USB 2.0 full speed (12Mbps) and low speed (1.5Mbps) operation. Automatic speed selection configures integrated pull-up resistors on the upstream port to match those sensed on the downstream device.

The isolator µModule technology uses coupled inductors and an isolated power transformer to provide 2500VRMS of isolation between the upstream and downstream USB interface. This device is ideal for systems requiring isolated ground returns or large common mode voltage variations. Uninterrupted communication is guaranteed for common mode transients greater than 30kV/μs.

Enhanced ESD protection allows this part to withstand up to ±15kV (human body model) on the USB transceiver interface pins to local supplies and ±15kV through the isolation barrier to supplies without latch-up or damage.

Powered 2.5W Isolated Hub Port

applicaTions

n Isolated USB Transceiver: 2500VRMS for 1 Minuten UL-CSA Recognized File #E151738n USB 2.0 Full Speed and Low Speed Compatiblen Integrated Isolated DC/DC Converter, External or

Bus Poweredn Auto-Configuration of Bus Speedn 2.5W (500mA at 5V) Output Power from External

Input Supply (VCC = 8.6V to 16.5V)n 1W (200mA at 5V) Output Power from USB Bus

Supply (VBUS)n 3.3V LDO Output Supply Signal References VLO, VLO2n High Common Mode Transient Immunity: 30kV/μsn ESD: ±15kV HBM on USB Interface Pinsn 15mm × 15mm × 5mm Surface Mount BGA Package

n Isolated USB Interfacesn Host, Hub, or Device Isolationn Industrial/Medical Data AcquisitionL, LT, LTC, LTM, Linear Technology, the Linear logo and µModule are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

Bus Powered 1W Isolated Peripheral Device

2884 TA01a

ISOL

ATIO

N BA

RRIE

R

VLO

LTM2884500mA AT 5V

ON

4.4V TO 16.5V

VBUS

VBUS2

8.6V TO 16.5V

100µF

VCC

SPNDPWR

D1+

D1–

VCC2

VLO2

D2+DOWNSTREAM

USB PORT

D2–

GND2GND15k 15k

+PWR

HUBµC

2884 TA01b

VLO

ON

SPNDPWR

VCC2

VBUS

VBUS

GND

GND2GND

UPSTREAMUSB PORT

VCC

ISOL

ATIO

N BA

RRIE

R

LTM2884

200mA AT 5V

D1+

PERIPHERAL

D1–

VLO2

D2+

D2–

PWR

1.5k

http://www.linear.com/LTM2884


LTM2884

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pin conFiguraTionabsoluTe MaxiMuM raTings

Supply Voltages VCC to GND ............................................ –0.3V to 18V VBUS to GND .......................................... –0.3V to 18V VCC2 to GND2 ....................................... –0.3V to 10V

VLO to GND .................................................. –0.3V to 4VVLO2 to GND2 ............................................... –0.3V to 4VON, SPNDPWR to GND .................–0.3V to (VLO + 0.3V)D1+, D1– to GND ........................................ –0.3V to 5.3VD2+, D2– to GND2 ..................................... –0.3V to 5.3VOperating Ambient Temperature Range (Note 3)

LTM2884C ............................................... 0°C to 70°C LTM2884I ............................................–40°C to 85°C LTM2884H ......................................... –40°C to 105°C

Storage Temperature Range .................. –55°C to 125°CMaximum Internal Operating Temperature ............ 125°CPeak Body Reflow Temperature ............................ 245°C

(Note 1)

BGA PACKAGE44-LEAD (15mm × 15mm × 5mm)

TOP VIEW

21 43 5 6 7 8 9 1110

D1– D1+ SPND-PWR ON VLO VBUS VCCGND

D2– D2+ VLO2 VCC2GND2

GND2

GND

GND2

F

G

H

L

J

K

E

A

B

C

D

TJMAX = 125°C,

PCB = JESD51-9 2s2p: θJA = 18.7°C/W, θJCtop = 16°C/W, θJCbottom = 5.7°C/W, θJB = 5.6°C/W PCB = DC1746A: θJA = 33.5°C/W, θJCtop = 15.7°C/W, θJCbottom = 6.1°C/W, θJB = 5.3°C/W

HEAT FLOW: θJA = NORMAL, θJCtop = 100%, θJCbottom = 100%, θJB = 100% WEIGHT = 2.4g

PART NUMBER PAD OR BALL FINISH

PART MARKING PACKAGE TYPE

MSL RATING TEMPERATURE RANGEDEVICE FINISH CODE

LTM2884CY#PBF

SAC305 (RoHS) LTM2884Y e1 BGA 4

0°C to 70°C

LTM2884IY#PBF –40°C to 85°C

LTM2884HY#PBF –40°C to 105°C

• Device temperature grade is indicated by a label on the shipping container.

• Pad or ball finish code is per IPC/JEDEC J-STD-609.• Terminal Finish Part Marking: www.linear.com/leadfree• This product is not recommended for second side reflow. For more

information, go to: www.linear.com/BGA-assy

• Recommended BGA PCB Assembly and Manufacturing Procedures: www.linear.com/BGA-assy

• BGA Package and Tray Drawings: www.linear.com/packaging• This product is moisture sensitive. For more information, go to:

www.linear.com/BGA-assy

orDer inForMaTion http://www.linear.com/product/LTM2884#orderinfo


http://www.linear.com/leadfree

http://www.linear.com/BGA-assy


http://www.linear.com/packaging


http://www.linear.com/product/LTM2884#orderinfo

LTM2884

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elecTrical characTerisTics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VBUS = 5V, GND = GND2 = 0V, ON = VLO, unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Power Supply

VCC Operating Supply Range (Isolated Power Input) l 4.4 12 16.5 V

VBUS Operating Supply Range (USB Bus Power Input) l 4.4 5 16.5 V

VCC Supply Current Power Off ON = 0V, VCC = 4.4V to 16.5V l 100 500 µA

ICC VCC Supply Current Power On ICC2 = 0mA, Figure 1 l 50 100 mA

VBUS Supply Current Power Off ON = 0V l 10 100 µA

IBUS VBUS Supply Current Power On IVLO = 0mA, Figure 1 l 6 9 mA

VBUS Supply Current Suspend Mode SPNDPWR = 3.3V USB Suspend Timeout SPNDPWR = 0, USB Suspend Timeout

l

l

1.5

500

2.0

µA

mA

VCC2 Regulated VCC2 Output Voltage, Loaded VCC = 4.4V, ICC2 = 200mA, Figure 1 VCC = 8.6V, ICC2 = 500mA, Figure 1

l

l

4.75 4.75

5 5

5.25 5.25

V V

VCC2 Source Current High Power Mode VCC = 8.6V, Figure 1 l 500 mA

VCC2 Source Current Bus Power Mode VCC = VBUS = 4.4V, Figure 1 l 200 mA

VLO VLO Regulated Output Voltage IVLO = 0mA to 10mA, Figure 1 l 3.15 3.3 3.45 V

VLO Output Voltage Maximum Current Figure 1 l 10 mA

VLO2 VLO2 Regulated Output Voltage IVLO2 = 0mA to 10mA, Figure 1 l 3.15 3.3 3.45 V

VLO2 Output Voltage Maximum Current Figure 1 l 10 mA

USB Input Levels (D1+, D1–, D2+, D2–)

VIH Single-Ended Input High Voltage l 2.0 V

VIL Single-Ended Input Low Voltage l 0.8 V

VHYS Single-Ended Input Hysteresis 200 mV

VDIFF Differential Input Sensitivity |(D1+ – D1–)| or |(D2+ – D2–)| l 0.2 V

VCM Common Mode Voltage Range |(D1+ + D1–)|/2 or |(D2+ + D2–)|/2 l 0.8 2.5 V

Logic Input Levels (ON, SPNDPWR)

VIHL Logic Input High Voltage l 2.0 V

VILL Logic Input Low Voltage l 0.8 V

IINL Logic Input Current l ±1 µA

VHYSL Logic Input Hysteresis 200 mV

USB Output Levels (D1+, D1–, D2+, D2–)

VOL Output Low Voltage RPU = 1.5k to 3.6V, Figure 4 l 0 0.3 V

VOH Output High Voltage RPD = 15k to 0V, Figure 4 l 2.8 3.6 V

VCRS Differential Output Signal Cross-Point Voltage l 1.3 2.0 V

Terminations

RPU Bus Pull-Up Resistance on Upstream Facing Port D2+ or D2– Pull-Up to 3.3V 1.425 1.575 kΩ

RPD Bus Pull-Down Resistance on Downstream Facing Port D2+ and D2– Pull-Down to GND2 14.25 15.75 kΩ

ZDRV USB Driver Output Resistance l 28 44 Ω

CINUSB USB Transceiver Pad Capacitance to GND (Note 2) 10 pF


LTM2884

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swiTching characTerisTics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VBUS = 5V, GND = GND2 = 0V, ON = VLO, unless otherwise noted.


Low Speed USB

tLDR Low Speed Data Rate CL = 50pF to 450pF (Note 4) 1.5 Mbps

tLR Rise Time Figure 2, CL = 50pF to 600pF l 75 300 ns

tLF Fall Time Figure 2, CL = 50pF to 600pF l 75 300 ns

tLPRR, tLPFF Propagation Delay Figure 2, CL = 50pF to 600pF l 200 300 ns

tLDJ1 Differential Jitter To Next Transition (Note 2) ±45 ns

tLDJ2 Differential Jitter To Paired Transitions (Note 2) ± 15 ns

Full Speed USB

tFDR Full Speed Data Rate CL = 50pF (Note 4) 12 Mbps

tFR Rise Time Figure 3, CL = 50pF l 4 20 ns

tFF Fall Time Figure 3, CL = 50pF l 4 20 ns

tFPRR, tFPFF Propagation Delay Figure 3, CL = 50pF l 60 80 115 ns

tFDJ1 Differential Jitter To Next Transition (Note 2) 2 ns

tFDJ2 Differential Jitter To Paired Transitions (Note 2) 1 ns

Power Supply Generator

VCC2 – GND2 Supply Start-Up Time (ON VLO, VCC2 to 4.5V)

RLOAD = 50Ω, CLOAD = 100µF RLOAD = 10Ω, CLOAD = 100µF, VCC = 12V

l

l

2 3

5 10

ms ms

tWUSPND Wake Up from Suspend Mode Resume Signal, SPNDPWR = 0 l 0.25 10 µs

ESD (HBM) (Note 2) Isolation Barrier GND to GND2 ±15 kV

D1+, D1–, D2+, D2– D1+/D1– to GND, VCC, VBUS, or VLO and D2+/D2– to GND2, VCC2, or VLO2

±15 kV

ON, SPNDPWR ±3 kV

isolaTion characTerisTics TA = 25°C.


Isolation Barrier: GND to GND2

VISO Rated Dielectric Insulation Voltage (Notes 6, 7)

1 Minute (Derived from 1 Second Test) 2500 VRMS

1 Second (Note 5) 3000 VRMS

Common Mode Transient Immunity VBUS = VCC = 5V, ON = 3.3V, 1000V in 33ns Transient Between GND and GND2 (Note 2)

±30 kV/µs

VIORM Maximum Working Insulation Voltage (Notes 2, 5) 560 400

VPEAK VRMS

Partial Discharge VPR = 750VRMS (Note 5) <5 pC

CTI Comparative Tracking Index IEC 60112 (Note 2) 600 VRMS

Depth of Erosion IEC 60112 (Note 2) 0.017 mm

DTI Distance Through Insulation (Note 2) 0.1 mm

Input to Output Resistance (Notes 2, 5) 1012 Ω

Input to Output Capacitance (Notes 2, 5) 13 pF

Creepage Distance (Notes 2, 5) 9.48 mm


LTM2884

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Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime.Note 2: Guaranteed by design and not production tested.Note 3: This µModule transceiver includes over temperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when over temperature protection is active. Continuous operation above specified maximum operating junction temperature may result in device degradation or failure.

Note 4: Maximum data rate is guaranteed by other measured parameters and is not directly tested.Note 5: Device considered a 2-terminal device. Measurement between groups of pins A1 through B11 shorted together and pins K1 through L11 shorted together.Note 6: The rated dielectric insulation voltage should not be interpreted as a continuous voltage rating.Note 7: In accordance with UL1577, each device is proof tested for the 2500VRMS rating by applying the equivalent positive and negative peak voltage multiplied by an acceleration factor of 1.2 for one second.

elecTrical characTerisTics


LTM2884

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Typical perForMance characTerisTics

Low Speed Differential JitterVCC2 Output Current vs Temperature

VCC to VCC2 Efficiency and Power Loss

VCC Input Current vs VCC2 Output Current

VCC2 Output Voltage vs Load Current

Full Speed Propagation Delay vs Temperature

Low Speed Propagation Delay vs Temperature Full Speed Differential Jitter

TA = 25°C, VCC = 5V, VBUS = 5V, GND = GND2 = 0V, ON = 3.3V, unless otherwise noted.

TEMPERATURE (°C)–50

PROP

AGAT

ION

DELA

Y (n

s)

100

95

75

90

85

80

70500 100

2884 G01

12525–25 75

CLOAD = 120pF


PROP

AGAT

ION

DELA

Y (n

s)

250

240

230

220

210

200500 100

2884 G02

12525–25 75

CLOAD = 120pF

10ns/DIV

1V/DIV

2884 G03

JITTER 1.4nsP-P

D1–

D1+

D2–

D2+

50ns/DIV

1V/DIV

2884 G04

JITTER 7.5nsP-P

D1+

D1–

D2+

D2–


OUTP

UT C

URRE

NT (m

A)

800

600

700

500

400

300

200500 100

2884 G05

12525–25 75

VCC = 12V

VCC = 5V

VCC2 = 4.75V

OUTPUT CURRENT (A)0

INPU

T CU

RREN

T (m

A)

450

350

400

300

150

200

100

250

50

00.2 0.6

2884 G07

0.80.4

VCC = 12VVCC = 5V

LOAD CURRENT (A)0

V CC2

(V)

5.25

4.75

5.00

4.50

4.25

4.000.40.2 0.8

2884 G08

1.00.6

VCC = 5V

VCC = 4.4V

VCC = 8.1V

VCC = 12V

IOUT (A)0

EFFI

CIEN

CY (%

)

POWER LOSS (W

)

70

50

60

40

30

20

0

1.4

1.2

0.8

1.0

0.6

0.4

0.2

00.2 0.6

2884 G06

0.80.4

VCC = 5V

VCC = 5V

VCC = 12V

VCC = 12V

POWER LOSS

EFFICIENCY

Derating for 125°C Maximum Internal Operating Temperature

TEMPERATURE (°C)25

LOAD

CUR

RENT

(A)

0.55

0.45

0.50

0.40

0.25

0.15

0.20

0.35

0.30

0.10

0.05

04535 55 7565 9585 115

2884 G09

125105

VBUS – VCC = 5VVBUS – VCC = 8.6VVBUS – VCC = 12VVBUS – VCC = 16.5V


LTM2884

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Typical perForMance characTerisTics

VCC2 = Load Step Response, 0mA to 500mA (VCC = 12V)

VCC2 = Load Step Response, 0mA to 200mA (VCC = 5V) ICC vs Temperature

Upstream VBUS Droop During Plug-In with CLOAD = 100µF Full Speed Data Start of Packet

VCC2 Ripple, VCC = 5V, ICC2 = 200mA VCC2 Start-Up Ramp

TA = 25°C, VCC = 5V, VBUS = 5V, GND = GND2 = 0V, ON = 3.3V, unless otherwise noted.

2µs/DIV

100mV/DIV

2884 G10

VCC2 Ripple, VCC = 12V, ICC2 = 500mA

100µs/DIV

500mV/DIV

200mA/DIV

2884 G13

VCC2

ICC2

100µs/DIV

500mV/DIV

200mA/DIV

2884 G14

VCC2

ICC2


SUPP

LY C

URRE

NT (m

A)

70

30

60

20

50

40

10

0–25 25 50 75 100

2884 G15

1250

VCC = 12.5V

VCC = 16.5V

VCC = 5V

VCC = 8.1V

VCC = 4.4VICC2 = 0mA

500µs/DIV

1V/DIV

2884 G16

ISOLATED VCC2

HOST VBUS

PLUG IN TO HOST

100ns/DIV

500mV/DIV

2884 G17

D2+

D2–

2µs/DIV

100mV/DIV

2884 G11 500µs/DIV

1V/DIV

2884 G12

ON

VCC2

VCC2 Droop/Plug-In Response

200µs/DIV

1V/DIV

2884 G16

VCC

VCC2


LTM2884

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pin FuncTionsUpstream Side (VCC, VBUS, VLO, GND)

D1– (A1): USB Data Bus Upstream Facing Negative Transceiver Pin. A 1.5k pull-up resistor is automatically configured to indicate the idle condition of the D2– pin.

D1+ (A2): USB Data Bus Upstream Facing Positive Transceiver Pin. A 1.5k pull-up resistor is automatically configured to indicate the idle condition of the D2+ pin.

SPNDPWR (A3): Suspend Power Control. A high input enables the DC/DC converter shutdown control if the USB bus is suspended. A low input (GND) disables the shut-down control to the DC/DC converter maintaining power to the isolated downstream side during suspend mode. The recovery time from suspend mode may be equivalent to the power supply start-up time if the DC/DC converter was shut down. The SPNDPWR pin is referenced to VLO and GND.

ON (A4): Enable for Power and Data Communication Through the Isolation Barrier. If ON is high, the part is enabled. If ON is low, the upstream side is held in reset and the isolated side is unpowered by the DC/DC converter. The ON pin is referenced between VLO and GND.

VLO (A5): Internally Regulated 3.3V Logic Voltage Output. The VLO pin is used as a positive reference for the ON and SPNDPWR pins and can source up to 10mA of surplus current. Internally bypassed to GND with 2.2µF. Output supply, no external connection necessary.

GND (A6, B1-B11): Upstream Circuit Ground.

VBUS (A7): Voltage Supply Input to USB Transceiver. The operating range is 4.4V to 16.5V. Connect to the USB VBUS supply or an external source. Internally bypassed to GND with 2.2µF.

VCC (A8-A11): Voltage Supply Input to DC/DC Converter. The operating range is 4.4V to 16.5V. Connect to an external supply greater than 8.6V for 500mA on VCC2,VBUS must be connected to the external supply or USB power. Connect to the USB VBUS for up to 200mA on VCC2. Connect VCC to VBUS when the peripheral device has an external power source. Internally bypassed to GND with 4.7µF.

Isolated Downstream Side (VCC2, VLO2, GND2)

GND2 (K1-K11, L3, L4, L6, L7): Downstream Circuit Ground.

D2– (L1): USB Data Bus Downstream Facing Negative Transceiver Pin. The pin has a 15k pull-down resistor to GND2.

D2+ (L2): USB Data Bus Downstream Facing Positive Trans-ceiver Pin. The pin has a 15k pull-down resistor to GND2.

VLO2 (L5): Internally Regulated 3.3V Logic Voltage Output. The VLO2 pin can source up to 10mA of surplus current. Internally bypassed to GND2 with 2.2µF. Output supply, no external connection necessary.

VCC2 (L8-L11): Isolated Voltage Supply Output from DC/DC Converter. Output voltage is 5V and can support up to 500mA of peripheral device current referenced to GND2. Output current is dependant on input supply voltage and current limit. Internally bypassed to GND2 with 22µF. Output supply, no external connection necessary.


LTM2884

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block DiagraM

2884 BD

22µF

D2+

VLO2

VCC2

15k

GND2GND

= UPSTREAM SIDE COMMON = DOWNSTREAM SIDE COMMON

15k

DOWNSTREAMPORTD2–

4.7µF

VCC

2.2µF

3.3VREG

3.3VREG

ISOLATED COMMUNICATIONINTERFACE

ISOLATED COMMUNICATIONINTERFACE

2.2µF

VBUS

VLO

ON

D1+

D1–

2.2µF

DC/DC

SPNDPWR

UPSTREAMPORT

1.5k 1.5k


LTM2884

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TesT circuiTs

2884 F01IS

OLAT

ION

BARR

IER

VCC

ICCLTM2884

VBUS

VBUS

VLO

IVLO

GND

VCC2

VLO2

GND2

IVLO2 ICC2+–VCC+–

IBUS

Figure 1. Power Supply Loads


LTM2884

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2884 F02

0V

3.3V

0V

3.3V

D1+ OR D2+ D2+ OR D1+

CL

D1– OR D2– D2– OR D1–

3.6V

CL

1.5k

tLR

tLPRR tLPFF

tLF

10% 10%

90% 90%

D2+ OR D1+

D2– OR D1–

D1+ OR D2+

D1– OR D2–

2884 F03

0V

3.3V

0V

3.3V

D1+ OR D2+ D2+ OR D1+

CL

D1– OR D2– D2– OR D1–

CL tFF

tFPFF tFPRR

tFR

10% 10%

90% 90%

D2– OR D1–

D2+ OR D1+

D1– OR D2–

D1+ OR D2+

Figure 2. Low Speed Timing Measurements

Figure 3. Full Speed Timing Measurements

TesT circuiTs


LTM2884

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FuncTional TableUSB Transceiver Functional Table

MODE D1+ D1–AUTOMATIC PULL-UP

CONNECTION D2+ D2– SPNDPWR

Full Speed (Idle) 1.5k Pull-Up Host Pull-Down D1+ Peripheral Pull-Up 15k Pull-Down X

Low Speed (Idle) Host Pull-Down 1.5k Pull-Up D1– 15k Pull-Down Peripheral Pull-Up X

Disconnected (Idle) Host Pull-Down Host Pull-Down None 15k Pull-Down 15k Pull-Down X

Suspend (Idle >3ms) Set at Device Connect Set at Device Connect Set at Device Connect Peripheral or 15k Peripheral or 15k 0

Suspend No Power (Idle >3ms)

Set at Device Connect Set at Device Connect Set at Device Connect 15k Pull-Down 15k Pull-Down 3.3V

D1 to D2 Data IN+ IN– Set at Device Connect OUT+ OUT– X

D2 to D1 Data OUT+ OUT– Set at Device Connect IN+ IN– X

Power Functional TableMODE ON SPNDPWR VCC VBUS DC/DC CONVERTER

Off 0 X X X OFF

On 3.3V X >4.4V >4.4V ON

On, Suspend (Idle >3ms) 3.3V 0 >4.4V >4.4V ON

On, Suspend (Idle >3ms), Power Off 3.3V 3.3V >4.4V >4.4V OFF

On, USB Transceiver Only Power Off 3.3V X 0 >4.4V OFF


LTM2884

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The LTM2884 µModule transceiver provides a galvanically isolated robust USB interface, powered by an integrated, regulated DC/DC converter, complete with decoupling capacitors. This flexible device can support a variety of USB configurations, either bus powered or externally powered. Applications include isolation in hosts, hubs, peripherals, or standalone inline bus splitters. Automati-cally configured pull-up resistors are included to represent the condition of the isolated downstream USB bus to the upstream USB bus. The LTM2884 is ideal for use in USB connections where grounds between upstream hub/host and downstream devices can take on different voltages. Isolation in the LTM2884 blocks high voltage differences and eliminates ground loops and is extremely tolerant of common mode transients between ground potentials. Error free operation is maintained through common mode events exceeding 30kV/µs providing excellent noise isolation.

The LTM2884 contains a fully integrated DC/DC converter including the transformer, so that no external components are necessary in many configurations. The upstream side contains a flyback converter that regulates the downstream output voltage through primary sensing techniques. The internal power solution is sufficient to support the trans-ceiver interface and supply up to 500mA at 5V through VCC2 to an attached device dependent on the supply voltage and available current on VCC.

The integrated USB transceivers on both sides of the iso-lation barrier support full and low speed modes defined in the USB 2.0 specification. The communication through the isolation barrier for USB is bidirectional and as such the LTM2884 determines data flow direction based on which side a start of packet (SOP) begins first. The direction of data is maintained until an end of packet (EOP) pattern is observed or a timeout occurs due to a lack of activity. The USB interface maintains a consistent propagation delay representative of a hub delay and transfers all data.

Pull-up resistors integrated in the upstream interface automatically indicate device connections and discon-nections. A downstream device connection automatically selects the proper pull-up resistor at the upstream facing port after sensing the idle state of the downstream device at connection time. Disconnection of a downstream device automatically releases the pull-up resistor on the upstream facing port allowing the upstream 15k pull-down resistors to pull the bus signals to a disconnect condition. This func-tion makes the LTM2884 ideal for host, hub, bus splitter, or peripheral device integration.

Isolator µModule Technology

The LTM2884 utilizes isolator µModule technology to translate signals and power across an isolation barrier. Signals on either side of the barrier are encoded into pulses and translated across the isolation boundary us-ing differential signaling through coreless transformers formed in the µModule substrate. This system, complete with data refresh, error checking, safe shutdown on fail, and extremely high common mode immunity, provides a robust solution for bidirectional signal isolation. The µModule technology provides the means to combine the isolated signaling with a USB transceiver and powerful isolated DC/DC converter in one small package.

USB Transceiver Pin Protection

The LTM2884 USB transceiver pins D1+, D1–, D2+, and D2– have protection from ESD and short-circuit faults. The transceiver pins withstand ±15KV HBM ESD events. Overcurrent circuitry on the transceiver pins monitor fault conditions from D1+ and D1– to GND, VLO, or VBUS and from D2+ and D2– to GND2, VLO2, or VCC2. A current detection circuit disables the transceiver pin if the pin sinks about 40mA for greater than 600ns. The VLO and VLO2 output supplies protect the USB transceiver pins from shorts to GND or GND2 respectively with a 40mA current limit.

operaTion


LTM2884

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USB Connectivity

The LTM2884 µModule transceiver connects directly to USB ports on the upstream side and the downstream side without the addition of external components. The trans-ceiver passes through all data and does not act as a hub or intelligent device. The bus lines are monitored for idle conditions, start of packet, and end of packet conditions to properly maintain bus speed and data direction. The series resistance, pull-up, and pull-down resistors are built into the LTM2884. The upstream facing USB port contains automatically configured 1.5k pull-up resistors which are switched in or out based on the downstream side peripheral device configuration. This implementation allows upstream reporting of the downstream bus speed and connection/disconnection conditions. Built-in 15k pull-down resistors are included from the D2+ and D2– signals to GND2 supporting the downstream bus configuration.

Monitoring the USB data pins, the LTM2884 detects a K-state to begin a data packet and set the data direction. The data is monitored for an end of packet signature and a finishing J-state before the bus is released. The data pay-load between the K-state and J-state is transferred through the LTM2884 isolator with a delay of approximately 80ns.

Idle State Communication and Automatic Speed Selection

The LTM2884 µModule transceiver maintains the condi-tions of the USB bus idle state by monitoring the down-stream side bus idle condition and refreshing the state across the isolation barrier at a consistent rate. Further-more, the LTM2884 monitors the speed of the downstream peripheral once connected and sets its own operation to match. Figure 4 shows the abbreviated circuitry of the automatic monitoring and reporting of the bus speeds. The D2+ or D2– signals are monitored for a connection to pull-ups on D2+ or D2– and the result is processed as full speed or low speed, otherwise disconnect. The idle state is communicated to the upstream side through a refresh transmission. The switches SW1 or SW2 are controlled based on the received information. SW1 is closed if D2+ is detected to have a pull-up and D2– was open. SW2 is closed if D2– is detected to have a pull-up and D2+ was open. Both SW1 and SW2 are opened if the downstream USB bus is disconnected. During a USB suspend, the pull-up resistor will maintain the condition prior to detecting the suspend command.

applicaTions inForMaTion

Figure 4. Idle State Automatic Resistor Setting

2884 F04

ISOL

ATIO

N BA

RRIE

R

LTM2884

REFRESH

VLO

D1+

RPU1.5k

RPU1.5k

SW1 SW2

D1–

15k15k

D2+

D2–

RPD15k

RPD15k

1.5k

FULLSPEED

UPSTREAM CONNECTION DOWNSTREAM CONNECTION

OR

OR DISCONNECTED

LOWSPEED

1.5k

3.3V 3.3V


LTM2884

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applicaTions inForMaTionSuspend Mode

When the upstream USB bus is idle for greater than 3ms, the LTM2884 enters suspend mode. The power savings and behavior in suspend mode depend on the state of the SPNDPWR pin, as summarized in Table 1.

Table 1. Suspend Mode Operation

SPNDPWR VCC2 IBUS ICC WAKE-UPWAKE-UP

TIME

High Off < 500µA VCC/45k Resume 3ms

Low On 1.5mA 50mA Resume or Remote Wake-Up

10µs

The biggest power savings in suspend mode comes when SPNDPWR is high. In this case, the DC/DC converter is disabled, shutting down power to the isolated side, while the current draw on VCC and VBUS are minimized. How-ever, in this mode, if a downstream device is connected or disconnected from the bus or remote wake-up functionality is configured, it will not be recognized by the LTM2884 and will not be relayed to the host. A resume command at the upstream side will wake up the LTM2884 and a re-numeration by the host will be required. Recovery time is about 3ms from the start of the resume command on the upstream side.

If SPNDPWR is low in suspend mode, the LTM2884 oper-ates in a low power mode but maintains a higher functional state with the DC/DC converter on and the downstream transceiver powered. The VBUS current is reduced to 1.5mA and VCC current is about 50mA when there is no external draw on VCC2. Wake-up is initiated with discon-nects, reconnects, or a remote wake-up command from a downstream device or a resume command from the host. Recovery time from suspend mode is about 10µs from when the first state change is detected.

During suspend mode DC current drawn from VLO into external circuits will be supplied from VBUS and may exceed the limits set in the USB specification.

DC/DC Power Supply

The internal DC/DC converter converts the input power from the VCC pin to the VCC2 output. The power delivered to the VCC2 pin is regulated and current limited to protect against overcurrent conditions. The voltage supply, VCC, is sensed to limit the maximum current that can be delivered before USB specifications are exceeded. Connecting the VCC and VBUS supply pins to the USB VBUS pin (4.4V to 5.5V) lim-its the maximum downstream side supply current to 200mA before VCC2 supply degradation. When VCC is connected to a high voltage external DC source (8.6V to 16.5V) the cur-rent limit is increased so that 500mA is sourced from VCC2. If a downstream device sinking current from VCC2 draws more than 25mA, the input current on VCC may exceed 100mA, the USB single unit load specification for low power devices. The LTM2884 does not enforce a 100mA current limit for low power peripherals.

VCC2 is internally decoupled to GND2 with a 22µF capaci-tor. Add an additional low ESR 100µF capacitor to VCC2 to meet the VBUS downstream supply decoupling minimum specification of 120µF when supporting device plug in. Locate the additional 100µF capacitor adjacent to the downstream USB connector. Additional capacitance may not be necessary when the LTM2884 is used in a peripheral device, or upstream hub application.

VLO and VLO2 Supplies

The VLO and VLO2 output supply pins are available for use as low current 3.3V supplies on both sides of the isolation barrier. They also serve as supplies for the USB interface circuitry. An internal linear regulator maintains 3.3V on VLO from the VBUS input supply. A separate linear regulator maintains 3.3V on VLO2 from VCC2. The current is limited to 10mA for external applications. Exceeding this limit may cause degradation in the VLO or VLO2 supplies and undesirable operation from the USB isolator. Connection of signals ON or SPNDPWR to VLO will not cause a significant change in the available VLO current. These supplies are available to support interface logic to the isolated USB port. In order to meet the suspend mode current limit, minimize the DC current of external applications on the VLO output supply. VLO and VLO2 are protected from overcurrent and overtemperature conditions.


LTM2884

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applicaTions inForMaTionSupply Current

Loading the multiple output supply pins of the LTM2884 affects the supply current on VBUS and VCC. The VBUS input supplies current to the the upstream side of the trans-ceiver and to the VLO pin. The VCC input supplies power to VCC2 and VLO2 through an isolated DC/DC converter. The efficiency (η) of the DC/DC converter is shown in the Typical Performance Characteristics section for 5V and 12V inputs from VCC to VCC2.

Supply Current Equations

Operating:

IBUS = 6mA + IVLO

ICC =VCC2 • 6mA + ICC2+ IVLO2( )

η • VCC

Suspend: SPNDPWR = 0

IBUS = 1.5mA + IVLO

ICC =VCC2 • 6mA + ICC2+ IVLO2( )

η • VCC

Suspend: SPNDPWR = VLO

IBUS = 0.45mA + IVLO

ICC =VCC45k

Off:

IBUS = 10µA

ICC = VCC45k

USB 2.0 Compatibility

The LTM2884 µModule transceiver is compatible with the USB 2.0 specification of full and low speed operation. Some characteristics and implementations may not support full compliance with the USB 2.0 specification. Three specific

cases exist within the LTM2884 µModule transceiver and the integrated DC/DC power converter.

First, the propagation delay for full speed data of 80ns exceeds the specification for a single hub of 44ns plus the attached cable delay of 26ns. This is due to driving the signal to the 3.3V rail prior to a K-state transition to maintain balanced crossover voltages equivalent to the cross over voltages of the successive data transitions. USB ports commonly drive the idle state bus to the 3.3V rail prior to the k-state start of packet transition.

Second, setting SPNDPWR = VLO will cause the DC/DC power converter to turn off during a bus suspend. VCC2 will lose power causing the downstream device to lose enumeration. Remote wake-up, disconnect, and recon-nect events are ignored. A resume command from the host or upstream hub will start the DC/DC converter and wake up the downstream device. The downstream device will require re-enumeration, which causes a failure in USB compliance testing. After a resume command initiates, a delay of 3ms will elapse before the isolated device is fully powered. When SPNDPWR = 0V, the DC/DC power converter remains on during suspend, therefore power and enumeration information is retained. The VCC supply consumes 50mA to support the isolated power during suspend. Separate the VBUS and VCC supplies to comply with the 2.5mA USB 2.0 VBUS suspend current specification.

Third, when connecting a low power device to the downstream side of the LTM2884 and VBUS and VCC are connected together, the input current is higher due to the operating current and the efficiency of the DC/DC converter. The operating current of the DC/DC converter and the USB transceiver function is 46mA. The efficiency of the converter is approximately 55%, resulting in a 1/0.55 increase in the input current due to the load current on VCC2. A 100mA load on VCC2 appears as a 181mA load + operating current at VBUS and VCC. In order to meet a 100mA input current, the VCC2 load current must be less than 25mA. This characteristic of an isolated supply may limit the use of the LTM2884 in bus powered hub applica-tions or downstream connection to a bus powered hub. Connect VCC to an external supply to mitigate this concern.


LTM2884

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applicaTions inForMaTionHot Plug Protection

The VCC and VBUS inputs are bypassed with low ESR ceramic capacitors. During a hot plug event, the supply inputs can overshoot the supplied voltage due to cable inductance. When using external power supply sources greater than 10V that can be hot plugged, add an ad-ditional 2.2µF tantalum capacitor with greater than 1Ω of ESR, or a ceramic capacitor with a series 1Ω resistor to the VCC input to reduce the possibility of exceeding absolute maximum ratings. Refer to Application Note 88, “Ceramic Capacitors Can Cause Overvoltage Transients,” for a detailed discussion of this problem.

PC Board Layout

The high integration of the LTM2884 makes PCB layout simple. However, to optimize its electrical isolation char-acteristics, EMI, and thermal performance, some layout considerations are necessary. The PCB layout in Figure 5 is a recommended configuration for a low EMI USB application. The following considerations optimize the performance of the LTM2884:

• Under loaded conditions, VCC and GND current exceed 700mA, VCC2 and GND2 current is up to 500mA. Use sufficient copper on the PCB to ensure resistive losses do not cause the supply voltage to drop below the minimum allowed level. The heavy copper traces will also help to reduce thermal stress and improve thermal conductivity.

• Input and output decoupling is not required on peripheral or hub inputs. Add additional low ESR capacitance to reduce noise induction on the power supply connec-tions. Hub/bus splitter outputs require an additional 100µF of low ESR capacitance.

• Do not place copper between the inner columns of pads on the top or bottom of the PCB. This area must remain open to withstand the rated isolation voltage and maintain the creepage distance.

RF, Magnetic Field Immunity

The isolator µModule technology used within the LTM2884 has been independently evaluated, and successfully passed the RF and magnetic field immunity testing requirements per European Standard EN 55024, in accordance with the following test standards:

EN 61000-4-3 Radiated, Radio-Frequency, Electromagnetic Field Immunity

EN 61000-4-8 Power Frequency Magnetic Field Immunity

EN 61000-4-9 Pulsed Magnetic Field Immunity

Tests were performed using an unshielded test card de-signed per the data sheet PCB layout recommendations. Specific limits per test are detailed in Table 2.

Table 2. Test Frequency Field StrengthEN 61000-4-3, Annex D, 80MHz to 1GHz 1.4MHz to 2GHz 2GHz to 2.7GHz

10V/m 3V/m 1V/m

EN 61000-4-8, Level 4 50Hz and 60Hz 30A/m

EN 61000-4-8, Level 5 60Hz 100A/m*

EN 61000-4-9, Level 5 Pulse 1000A/m

*Non IEC Method

EMI

Radiated emissions have been measured for the LTM2884 using a gigahertz transverse electromagnetic (GTEM) cell with and without a USB cable attached. The performance shown in Figure 6 was achieved with the layout structure in Figure 5. Results are corrected per IEC 61000-4-20.


LTM2884

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applicaTions inForMaTion

Figure 5. PC Board Layout

Figure 6. EMI Plot

FREQUENCY (MHz)0

dBµV

/m

60

50

–20

40

30

20

10

–10

–30400200 600

2884 F06

1000300100 500 700 900800

0

CISPR 22 CLASS B LIMIT

DETECTOR = PEAK-HOLDRBW = 120kHzVBW= 300kHzSWEEP TIME = 680ms# OF POINTS = 501

2884 F04

TECHNOLOGY

DC1789a Demo Board

DC1789a Top DC1789a Bottom


LTM2884

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Typical applicaTions

Figure 7. Bus Powered Inline Bus Splitter

Figure 8. USB Hub Upstream Isolator

2884 F08

VLO

ON

SPNDPWR

UPSTREAM TOUSB HOST

VCC2

5V

VBUS

VBUS

GND

VCC

ISOL

ATIO

N BA

RRIE

R

LTM2884

D1+

D1–

VLO2

D2+

D2–

GND2GND

PWRUSB HUB

CONTROLLER

DA+

DA–

DB+

DB–

DC+

DC–

4 USBDOWNSTREAMPORTS

DD+

DD–

GND2

D+

D–

2884 F07

VLO

ON

SPNDPWR

VCC2 VBUS2

VBUS

VBUS

100mAOR 500mA

GND

VCC

ISOL

ATIO

N BA

RRIE

R

LTM2884

5V25mA

OR200mA

100µF

ISOLATEDDOWNSTREAMUSB PORT

D1+

UPSTREAMUSB PORT

D1–

D+

D–

VLO2

D2+

D2–D+

D–

GND2GND2GND

PWR


LTM2884

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Figure 9. USB Host Integration

Figure 10. Powered Peripheral Device with USB Isolation and Low Current Suspend

2884 F09

VLO

ON

SPNDPWR

VCC2 VBUS2

VBUS

GND

VCC

4.4V TO 16.5V

ISOL

ATIO

N BA

RRIE

R

USB HOSTCONTROLLER

LTM2884

5V UP TO200mA FOR VCC 4.4V TO 5.5V500mA FOR VCC 8.6V TO 16.5V

100µF

D1+

D1–

15k

VLO2

D2+

D2–D+

DOWNSTREAMUSB PORT

D–

GND2 GND2

PWR

15k

2884 F10

VLO

ON

SPNDPWR

VCC2

VBUS

VBUS

GND

VCC

ISOL

ATIO

N BA

RRIE

R

LTM2884

D1+

D1–

D+

UPSTREAMUSB PORT

D–

VLO2

D2+

D2–

GND2GND

PWRPERIPHERAL

5V


LTM2884

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Figure 11. Bus or Self Powered USB Isolation with Low Current Suspend and Power Plug Detection

2884 F11

VLO

ON

SPNDPWR

VCC2

VBUS

GND

VCC

ISOL

ATIO

N BA

RRIE

R

LTM2884

D1+

D1–

D+

UPSTREAMUSB PORT

D–

VLO2

D2+

D2–

GND2GND

PWRPERIPHERAL

200mA FOR VCC 4.4V TO 5.5V500mA FOR VCC 8.6V TO 16.5V

VINGNDCTL

SENSEGATESTAT

LTC4412

VINSHDNUVOV

4.75k

4.99k

150k

GATEVOUTFAULT

GND

LTC4365

OVERVOLTAGE = 16.7VUNDERVOLTAGE = 8.1V

9V TO 16V (500mA) Si4230DY-TI-GE3

SiA921EDJ

VPLUG

VBUS

Figure 12. Isolated 1W or 2.5W Power Supply

2884 F12

VLO

ON

SPNDPWR

VCC2

VBUS

VPLUG

GND

VCC

ISOL

ATIO

N BA

RRIE

R

LTM2884

D1+

D1–

VLO2

D2+

D2–

GND2GND

PWR

200mA FOR VCC 4.4V TO 5.5V500mA FOR VCC 8.6V TO 16.5V

4.4V TO 16.5V (500mA)

OFFON

5V


LTM2884

222884fb


Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

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package DescripTionPlease refer to http://www.linear.com/product/LTM2884#packaging for the most recent package drawings.


http://www.linear.com/product/LTM2884#packaging

LTM2884

232884fb


revision hisToryREV DATE DESCRIPTION PAGE NUMBER

A 08/16 Added UL-CSA logo in Features list 1

B 11/16 Lowered Storage Temperature to –55°C 2


LTM2884

242884fb

For more information www.linear.com/LTM2884 LINEAR TECHNOLOGY CORPORATION 2014

LT 1116 REV B • PRINTED IN USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417(408) 432-1900 FAX: (408) 434-0507 www.linear.com/LTM2884

relaTeD parTs

Typical applicaTion

PART NUMBER DESCRIPTION COMMENTSLTM2881 Complete Isolated RS485/RS422 µModule Transceiver + Power 2500VRMS Isolation in Surface Mount BGA or LGALTM2882 Dual Isolated RS232 µModule Transceiver with Integrated DC/DC Converter 2500VRMS Isolation in Surface Mount BGA or LGALTM2883 SPI or I2C µModule Isolator with Adjustable ±12.5V and 5V Regulated Power 2500VRMS Isolation in Surface Mount BGALTM2892 SPI/Digital or I2C µModule Isolator 3500VRMS Isolation, 6 ChannelsLTM2894 USB µModule Isolator 7500VRMS Isolation

Figure 13. Self Powered 4-Port Hub with Independent Isolation2884 F13

VBUS12V

VLO

VCC

ON

SPNDPWRGND

ISOL

ATIO

N BA

RRIE

R

LTM2884

D4D–

D4D+

D3C–

D3C+

VLO2

VCC2 VBUSA

GND2

D2+

D2–DA+

DA–

PWR

USB PORT A

100µF

VBUS12V

VLO

D2+

D2–

VCC

ON

SPNDPWRGND

ISOL

ATIO

N BA

RRIE

R

LTM2884

VLO2

VCC2 VBUSB

GND2

DB+

DB–

PWR

USB PORT B

100µF

VBUS12V

VLO

VCC

ON

SPNDPWRGND

ISOL

ATIO

N BA

RRIE

R

LTM2884

VLO2

VCC2 VBUSC

GND2

DC+

DC–

PWR

USB PORT C

100µF

VBUS12V

VLO

VCC

0.2Ω51k

1.5k

91k

4.7µF4.7µF

0.2Ω

ON

15k

27Ω

27Ω

SN74LVC04

SPNDPWRGND

ISOL

ATIO

N BA

RRIE

R

LTM2884

D1–

D1+

D1–

D1+

D2B–

D2B+

D1–

D1+

D1A–

PWRON_A

PWRON_B

PWRON_C

PWRON_D

D1A+

D1–

D1+

VLO2

VCC2 VBUSD

GNDD

GNDC

GNDB

GNDA

GND2

DD+

DD–

PWR

USB PORT D

100µF

STATUSENSDIN

VSDS

GATEGND

LTC1154

12V

27Ω

27Ω

3.3V

3.3V47k

3.3V

15k

15k

27Ω

27Ω

STATUSENSDIN

VSDS

GATEGND

LTC1154

6MHz CLOCKSIGNAL

SYSTEMPOWER-ON

RESET

12V

15k

0.2Ω

15k

27Ω

27Ω

STATUSENSDIN

VSDS

GATEGND

LTC1154

12V

15k

0.2Ω

15k

27Ω

27Ω

STATUSENSDIN

VSDS

GATEGND

LTC1154

12V

15k

OVRCUR4

PWRON4

DP4

DM4DP0

DM0

DP0

VBUS

DM0

OVRCUR3

EXTMEM

VCC12V

GND

PWRON3

DP3

DM3

XTAL1

XTAL2

OVRCUR2

RESET

BUSPWR

EEDATA/GANGED

GND

PWRON2

DP2

DM2

OVRCUR1

PWRON1

DP1

DM1

SN75240

MAX4594 SPST

GND

NOCOM

IN

V+

3.3V LDOLT1762-3.3

AB

CD

TUSB2046B3.3V

51k

3.3V

51k

3.3V

51k

3.3V

D2+

D2–

D2+

D2–








ltm2884 – isolated usb transceiver with isolated power€¦ · vlo2 vlo2 regulated output voltage...

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